The main objective is to delineate the contribution of normally occurring embryonic sensory stimulation to postnatal species-specific auditory perception in several species of ducklings. This will be accomplished by taking away or adding to normally occurring embryonic auditory stimulation and measuring the effects of such manipulations on the embryo's and hatchling's species-specific perceptual discrimination ability. BIBLIOGRAPHIC REFERENCES: Gottlieb, G. Development of species identification in ducklings. I. Nature of perceptual deficit caused by embryonic auditory deprivation. J. comp. physiol. Psychol., 1975, 89, 387-399. Gottlieb, G. Ibid, II. Experiental prevention of perceptual deficit caused by embryonic auditory deprivation. J. comp. physiol. Psychol., 1975, 89, 675-684.